There is a need for an energy-efficient way to generate hydrogen from water.
Mor and coworkers report the use of highly ordered titania nanotube arrays of variable wall thickness to photocleave water under ultraviolet irradiation (G. K. Mor et al., “Enhanced Photocleavage of Water Using Titania Nanotube Arrays,” Nanoletters 5 (2005) p. 191-195). Visible-light-driven photocatalysts have been developed through band engineering by doping of metal cations into oxide semiconductors (A. Kudo, H. Kato, and I. Tsuji, “Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting,” Chem. Lett. 33 (2004) p. 1534-1539, and Z. Zou et al., “Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst,” Nature 414 (2001) p. 625-627) and by making solid solutions between ZnS and narrow band gap semiconductors (A. Kudo, H. Kato, and I. Tsuji, “Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting,” Chem. Lett. 33 (2004) p. 1534-1539). A nanocrystalline BiVO4 film electrode on conducting glass has been used for the decomposition of water under visible light (K. Sayama et al., “Photoelectrochemical decomposition of water on nanocrystalline BiVO4 film electrodes under visible light,” Chem. Comm. 2003 (2003) p. 2908-2909). The stoichiometric splitting of water into H2 and O2 under visible light irradiation has been performed using a mixture of Pt-WO3 and Pt—SrTiO3 (Cr—Ta-doped) photocatalysts and an IO3−/I− shuttle redox mediator (K. Sayama et al., “Stoichiometric water splitting into H2 and O2 using a mixture of two different photocatalysts and an IO3−/I− shuttle redox mediator under visible light irradiation,” Chem. Commun. 2001 (2001) p. 2416-2417).
Lindsey and Loewe (U.S. Pat. No. 6,603,070) reports the synthesis of light harvesting rods comprising covalently coupled porphyrinic macrocycles. Light harvesting arrays and solar cells containing the light harvesting rods are also described.
Gratzel, Kiwi, Kalyanasundaram, and Philp (U.S. Pat. No. 4,382,846) reports a method for the simultaneous production of hydrogen and oxygen from water by the visible light irradiation of a water solution containing photosensitizer, an electron relay, and a suitable combination of redox catalysts.